Detection of agricultural contraband in baggage

Abstract

A radiant energy imaging system for selectively enhancing the image of objects having circular cross section to distinguish them from the image of objects having rectangular cross section, such objects being contained in a material having a different density-absorption coefficient product than the objects. In the invention, the gradient image of the spatially resolved transmitted intensity of the radiation is calculated and eroded to preferentially remove the edges of images of objects having rectangular cross section. The invention finds particular use in detecting agricultural contraband contained in baggage or parcels.

Having thus described my invention, I claim: 
     
       1. In a radiant energy imaging system, a method for distinguishing objects having circular cross section from objects having rectangular cross section, such objects being contained in a material having a different density-absorption coefficient product than the objects, comprising: (a) directing a beam of radiant energy through the objects;   (b) measuring transmitted intensity of the radition while maintaining spatial resolution;   (c) calculating a spatial gradient image of the transmitted intensity;   (d) eroding the gradient image one or more times to preferentially remove edges of images of objects having rectangular cross section relative to edges of images of objects having circular cross section, said objects being contained in a material having a different density-absorption coefficient product than said objects; and   (e) presenting the image of step (d).   
     
     
       2. The method of claim 1 wherein step (b) furher comprises transforming the measured transmitted intensity with a point transform selected from the group consisting of full gamma correction, partial gamma correction, black/white reversal, and thresholding. 
     
     
       3. The method of claim 1 wherein step (d) further comprises multiplying the eroded gradient image by a constant. 
     
     
       4. The method of claim 3 wherein said multiplication comprises a false color transform. 
     
     
       5. The method of claim 1 wherein said step (d) further comprises thresholding the eroded gradient image. 
     
     
       6. The method of claim 1 further comprising adding the eroded gradient image of step (d) to the image of the spatially resolved transmitted intensity of step (b) prior to presenting the image. 
     
     
       7. The method of claim 6 wherein the eroded gradient image of step (d) is multiplied by a constant prior to being added to the image of step (b). 
     
     
       8. The method of claim 1 wherein said presenting of step (e) comprises visually displaying the image. 
     
     
       9. The method of claim 1 wherein said presenting of step (e) comprises integrating the eroded gradient image of step (d) and comparing the integrated value to a set value to activate an alarm. 
     
     
       10. The method of claim 1 wherein the objects having circular cross section are agricultural objects. 
     
     
       11. The method of claim 1 wherein the objects having circular cross section are voids. 
     
     
       12. In a radiant energy imaging system, a method for distinguishing objects having circular cross section from objects having rectangular cross section, such objects being contained in a material having a different density-absorption coefficient product than the objects, comprising: (a) directing a beam of radiant energy through the objects;   (b) measuring transmitted intensity of the radiation while maintaining spatial resolution;   (c) transforming the measured transmitted intensity of step (b) with a point transform selected from group consisting of full gamma correction, partial gamma correction, black/white reversal, and thresholding;   (d) calculating the spatial gradient image of the transformed transmitted intensity;   (e) eroding the gradient image one or more times to preferentially remove the edges of images of objects having rectangular cross section relative to the edges of images of objects having circular cross section, said objects being contained in a material having a different density-absorption coefficient product than said objects;   (f) multiplying the eroded gradient image by a constant;   (g) adding the eroded gradient image of step (f) to the image of the transformed spatially resolved transmitted intensity of step (c); and   (h) visually displaying the image of step (g).   
     
     
       13. A radiant energy imaging apparatus for distinguishing objects having circular cross section from objects having rectangular cross section, such objects being contained in a material having a different density-absorption coefficient product than the objects, comprising: (a) a beam of radiant energy to irradiate the objects;   (b) means for measuring transmitted intensity of the radiation after irradiation of the objects in step (a) while maintaining spatial resolution;   (c) means for calculating a spatial gradient image of the transmitted intensity of step (b);   (d) means for eroding the gradient image of step (c) one or more times to preferentially remove edges of images of objects having rectangular cross section relative to edges of images of objects having circular cross section; and   (e) means for presenting the image of step (d).   
     
     
       14. The apparatus of claim 13 wherein said measuring means of step (b) further comprises means for transforming the measured transmitted intensity with a point transform selected from the group consisting of full gamma correction, partial gamma correction, black/white reversal, and thresholding. 
     
     
       15. The apparatus of claim 13 wherein said eroding means of step (d) further comprises means for multiplying the eroded gradient image by a constant. 
     
     
       16. The apparatus of claim 13 further comprising means for thresholding the eroded gradient image. 
     
     
       17. The apparatus of claim 13 further comprising means for adding the eroded gradient image of step (d) to the image of the spatially resolved transmitted intensity of step (b) prior to presenting the image. 
     
     
       18. The apparatus of claim 13 wherein said means for presenting of step (e) comprises visually displaying the image. 
     
     
       19. The apparatus of claim 13 wherein said means for presenting of step (e) comprises integrating the eroded gradient image of step (d) and comparing the integrated value to a set value to activate an alarm.